The U.S. Air Force is investigating whether the On-Board Oxygen Generating System (OBOGS) found on several U.S. Air Force warplanes, including the F-22 Raptor, might be defective.

"Air Force operational commanders have temporarily restricted F-22 flight operations to an altitude at or below 25,000 feet for routine training missions," said Col. William Nichols, a spokesman for the command, which is responsible for training and equipping the service's combat air forces.

"Air Combat Command is conducting an investigation to assess on-board oxygen generating systems on several platforms, including the F-22," Nichols said. "The investigation is designed for mishap prevention and is a prudent measure to ensure the OBOGS are operating safely.

"When the investigation is completed, the results will be reviewed and appropriate actions, if warranted, will be taken," he said.

A Lockheed Martin spokesman confirmed that the restriction has been in place ever since an F-22 based at Elmendorf Air Force Base, Alaska, crashed in November. Lockheed is the prime contractor for the F-22, a next-generation stealth fighter jet.

One Air Force source said that an OBOGS malfunction might have been responsible for the incident, which resulted in the death of Capt. Jeffery Haney, an F-22 pilot assigned to the 525th Fighter Squadron.

Despite the restrictions, the Raptor remains fully operational and could carry out combat tasks if needed, he said.

"A standard safety practice with all aircraft is, if there is a known or suspected problem, you take measures to fix it," said Mark Gunzinger, an analyst at the Center for Strategic and Budgetary Assessments, Washington, and a former Air Force pilot. "It's not something you want to do, but these things happen with complex aircraft."

While the stealth fighter might be restricted in training operations, that does not mean the Raptor would be restricted during wartime missions, Gunzinger said.

"If it's a war, if it's truly a safety-of-flight issue and it's going to hurt pilots and it's going to prevent the mission from being accomplished, then obviously the restriction will stand," he said. "But if it's something of a temporary nature or there is a work-around in time of war, it may not impact combat operations."

An OBOGS malfunction can be potentially life-threatening, said Hans Weber, who sat on the U.S. Federal Aviation Administration's Research, Engineering and Development Advisory Committee, and is the current president of Tecop International, a San Diego consulting firm.

"It's a big deal if you're at high altitude and you run out of oxygen," Weber said.

At 50,000 feet, a human being has less than 10 seconds of useful consciousness, he said. The 25,000-foot altitude restriction would allow the pilot to quickly dive below 18,000 feet, where the atmosphere has enough oxygen to ensure prolonged survival in case of an emergency.

"It would take you so long when you're way up high, you may black out before you make it to a safe altitude," Weber said.

Given the nature of the restriction, the problem with the OBOGS is likely to be a reliability issue, Weber said. While the probability of malfunction is fairly low, it is not something aviators take lightly, he said.

Weber also said that equipment such as the OBOGS is fairly standardized across multiple aircraft types, which means aircraft other than the F-22 likely are also affected, which Air Combat Command acknowledges.

That makes me wonder whether there isn't an emergency oxgenbottle available? Hard to imaging for an aircraft regularly operating at high altitudes! Is the pilot supposed to die if he has to punch out at that altitude? Isn't there an oxygen bottle integrated into the seat which kicks in if the OBOGS should fail as well?

Scorpion82 wrote:That makes me wonder whether there isn't an emergency oxgenbottle available? Hard to imaging for an aircraft regularly operating at high altitudes! Is the pilot supposed to die if he has to punch out at that altitude? Isn't there an oxygen bottle integrated into the seat which kicks in if the OBOGS should fail as well?

The F-16 certainly has an oxygen bottle on the seat, so I'm sure the others do too. In my days we had to do a 180 day check and a 60 hour check of the LOX converter in the cockpit to ensure proper operations at various altitudes. The altitudes were simulated.

If the F-16 have one, the F-22 should have one as well. They both use the ACES II, albeit the one on the F-22 is a modified version. Maybe it have failed to kick in when the OBOGS failed or is there no automatism?

I guess the seat bottle is reserved for the ejection, as you would not want to be in a position where you have used the bottle as a spare and then have to eject and need it. I know there were incidents with the F-104G where at least two crashed due to the very same LOX converter used in the F-16. I believe it was these crashes that lead to the 60 day check.

Scorpion82 wrote:If the F-16 have one, the F-22 should have one as well. They both use the ACES II, albeit the one on the F-22 is a modified version. Maybe it have failed to kick in when the OBOGS failed or is there no automatism?

If he was already completely passed out from hypoxia then I suspect there was little time. IIRC, he ejected late. He probably woke up in a screaming (literally) dive and pulled the handles too late. note: pure speculation on my part

Scorpion82 wrote:If that's the case they should consider this option as a back up. Sometimes hard to believe that something like that may not have been considered as a possible risk, if it is this way.

At anytime a pilot believes he is hypoxic he can pull little green apple an get some fresh air. At least I beleive that to be the case as I've never been in a Raptor cockpit.

lamoey wrote:I guess the seat bottle is reserved for the ejection, as you would not want to be in a position where you have used the bottle as a spare and then have to eject and need it. I know there were incidents with the F-104G where at least two crashed due to the very same LOX converter used in the F-16. I believe it was these crashes that lead to the 60 day check.

If for any reason you have to use the spare in the seat, you immediately descend to an altitude where supplemental oxygen would not be required.

jeffb wrote:Wouldn't there also be a little blinking light on the dash to tell the pilot his air's gone bad?

Just like the F-16, the pilot can use the Emergency Oxygen Bottle on the side of the seat. And they do use it from time to time, but when they do they usually return to base because after using the bottle on the side of the seat, they wouldn't have any oxygen left to use if they had to eject.

jeffb wrote:Wouldn't there also be a little blinking light on the dash to tell the pilot his air's gone bad?

There is no "blinking light" on the forward console for OBOGS. There is a flow indicator on the BRAG valve, however, and the pilot would notice a loss of flow to his mask. He would also hear an audible "deedle deedle" and see an OBOGS ICAW on his left UFD.